February 6, 2014

Wildfires Could Help Explain A Warm Ancient Earth

According to a new study published in the journal Geophysical Research Letters, wildfires could explain why the Earth was so hot three million years ago.

Researchers at Yale University found that volatile compounds released by ancient Earth’s forests and smoke from wildfires caused more global warming than atmospheric levels of carbon dioxide. This study provides evidence that dynamic atmospheric chemistry is a culprit behind this warm ancient climate.

Nadine Unger of the Yale School of Forestry & Environmental Studies (F&ES) and colleagues used an Earth system model to determine the concentrations of tropospheric ozone, aerosol particles, and methane during the mid-Pliocene epoch. They found that these compounds were twice the levels observed in the pre-industrial era because so much more of the planet was covered in forest.

The researchers say that those reactive compounds altered Earth’s radiation balance, helping to contribute to global warming by two to three times more than carbon dioxide. This finding explains why the Earth was 3.6 to 5.4 degrees Fahrenheit warmer than the pre-industrial era despite atmospheric levels of carbon dioxide being about the same as today.

“The discovery is important for better understanding climate change throughout Earth’s history, and has enormous implications for the impacts of deforestation and the role of forests in climate protection strategies,” said Unger, an assistant professor of atmospheric chemistry at Yale.

She said the traditional view is that forests affect climate through carbon storage and by altering the color of the planet’s surface, influencing the albedo effect. However, the researchers discovered that there are other ways a forest ecosystem could impact the climate.

Some scientists believe that the Pliocene epoch is not only a snapshot of Earth’s past, but could be an example of Earth’s future.

The team used the NASA Goddard Institute for Space Studies Model-E2 global Earth system model to simulate the terrestrial ecosystem emissions and atmospheric chemical composition of the Pliocene and the pre-industrial era. They saw an increase in global vegetation that was the dominant drive of emissions during the Pliocene, which had subsequent effects on climate.

Previous studies dismissed this idea, claiming that these compounds would have limited impact on the climate because they would be washed away from the atmosphere by frequent rainfall. However, the new study says that the particles lingered about the same length of time when compared to the pre-industrial era.

“We might do a lot of work to reduce air pollution from road vehicle and industrial emissions, but in a warmer future world the natural ecosystems are just going to bring the ozone and aerosol particles right back,” Unger said. “Reducing and preventing the accumulation of fossil-fuel CO2 is the only way to ensure a safe climate future now.”